The present invention relates in general to steady rests for chucking and/or hold rod-shaped workpieces of circular diameter in a lathe, and in particular to a new and useful steady rest with three holding members disposed in a common plane, their respective points of contact being equidistant from the workpiece axis, with two of the holding members designed as pivoted angular levers disposed in mirror image relative to each other, and there being inserted between them a third holding member which is rectilinearly movable in a direction towards the workpiece axis by an actuating piston which can be acted upon by a pressure medium. The third holding member supports an adjusting member in the form of a vee or wedge provided with control surfaces and interacting with the free ends of the angular levers. A device is also provided for the compensation of the elastic deformations of the holding members.
A self-centering steady rest of this kind is known from German Pat. No. 33 14 483. In order to prevent a displacement of the workpiece under different chucking pressures, this steady rest has, for the compensation of the deflection of the outer holding members, an elastically resilient part installed in the central holding member. This elastically resilient part is in the form of an axially deformable rod or a belleville washer with largely linear deformation characteristics whose change in length equals the deflection. However, this embodiment of a device for the compensation of the elastic deformation of the holding members is not practical because the central holding member equipped with the elastically resilient part is no longer rigid, thus making vibrations having an adverse effect on the machining of the workpiece unavoidable and, because the actual deformation of the elastically resilient part is not definable. Consequently, the elastic deformation of the holding members can be influenced only inadequately, if at all, with this device which also is not adjustable.